Application of a multi-layer antireflective film on a plastic lens with use of an ion-assisted method is known. As an example of this, in Examples 7 to 10 of Patent Document 1, it is described that an ion-assisted method is used for forming all layers of films (high-refractive-index layers and low-refractive-index layers) that constitute a multi-layer antireflective film. In doing this, the film formation conditions (i.e. set values for acceleration voltage, acceleration current, and flow rate of gas to be used) according to the ion-assisted method are different for a high-refractive-index layer and a low-refractive-index layer, both of which constitute the multi-layer antireflective film.    [Patent Document 1] Japanese Patent Application Laid Open No. 2004-206024